Normally a mobile communication system has been developed for the purpose of providing a communication based on user's mobility. With the rapid growth of technologies, this mobile communication system has reached a stage capable of offering a high-speed data communication service beyond a voice communication.
Recently the standardization of LTE-A (Long Term Evolution-Advanced), which is one of next-generation mobile communication systems, has been performed in 3GPP. Targeting complete standardization around the late 2010, LTE-A has realized a high-rate packet-based communication having a higher transmission rate than a previous available data transmission rate.
With the progress of 3GPP standards, a solution to the simple optimization of a radio network has been discussed in addition to a solution to the increase of communication speed. Generally, at the initial construction of a radio network or at the network optimization, a base station or base station controller should collect radio environment information about its own cell coverage. This is referred to as a drive test.
A typical drive test is very time-consuming and laborious task that requires an operator to carry measurement equipment on a vehicle and to repeatedly conduct a measurement process for a long time. Measurement results are analyzed and then used to configure system parameters of a base station or base station controller. Such a drive test increases radio network optimization costs and operation costs, incurring much time consumption.
Therefore, studies of minimizing a drive test and of improving a radio environment analysis process and manual configuration are made in the name of MDT (Minimization of Drive Test). Specifically, the terminal that measures a radio channel transmits radio channel measurement information to the base station periodically or immediately in response to a specific event or after a predetermined time has elapsed from the time point when the radio channel measurement information is logged.
This operation, performed at the terminal, of transmitting the radio cell measurement information and any other additional information to the base station may be referred to as an MDT measurement information report. If a communication with the base station is available, the terminal transmits the channel measurement results to the base station immediately. If an immediate report is unavailable, the terminal logs the MDT measurement information and, when a communication becomes available, reports the logged MDT measurement information to the base station. Then, for the cell area optimization, the base station uses the MDT measurement information received from the terminal.
By the way, in MDT, the terminal performs measurements in an idle mode after establishing a connection with the network and receiving measurement-related configuration information. Therefore, in case of a failure in connection with the network, the terminal neither performs measurements nor transmits measurement information. However, the network may need measured information associated with a connection failure.